i965/fs: Perform CSE on MOV ..., VF instructions.
i965/fs: Perform CSE on MOV ..., VF instructions.

Safe from causing optimization loops, since we don't constant propagate
VF arguments.

(for this and the previous patch):
total instructions in shared programs: 4289075 -> 4271932 (-0.40%)
instructions in affected programs:     1616779 -> 1599636 (-1.06%)

Reviewed-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler